SET_SURFACE_TENSION

This command enters a distance- and velocity-dependent function which is added to the Gibbs energy of the phase at left side of each phase interface. This can then be used to emulate the effect of surface tension on the equilibrium between at the phase interface or limited phase mobility.

Syntax	set_surface_tension
Prompt	Function Enter a surface energy function which adds to the Gibbs Energy expression for the phase located at the lower (left) side of the interface. The expression is multiplied with the volume per mole substitional atoms. This command is also used to simulate a limited interfacial mobility control where the energy function is a function of the interface velocity. It is used to enter the surface energy to enable coarsening. However, it can also be used to simulate a case with a limited interfacial mobility.
	This function should only be used in spherical geometries if the function is solely dependent of the interface position. Function describing how the (surface) energy function varies with the particle radius and/or the interface velocity. The classical expression for the surface energy contribution has the form of . The molar volume should be given relative to the molar volume used by default in DICTRA, 1 x 10^-5 (m³/mole). The volume should also be given per mole of substitutional atoms. For a precipitate of type M_xC_y this means multiplying with a factor (y+x)/x. If we use M₆C as an example with surface tension 0.5 (J/m²) and molar volume of 0.71 x 10^-5 (m³/mole), the entered function should be 20.50.71(7/6)/X; Commonly the surface tension function is defined as: delta-G = 2 SIGMA * Vm / R The function to be entered will then be: 2SIGMA/X; A limited interface mobility can be expressed as: delta-G = v Vm /const The function to be entered is then: v/"const"; The expression is multiplied by the partial molar volume of the substitutional components.

Syntax

set_surface_tension

Prompt

Function

Enter a surface energy function which adds to the Gibbs Energy expression for the phase located at the lower (left) side of the interface. The expression is multiplied with the volume per mole substitional atoms. This command is also used to simulate a limited interfacial mobility control where the energy function is a function of the interface velocity.

It is used to enter the surface energy to enable coarsening. However, it can also be used to simulate a case with a limited interfacial mobility.

This function should only be used in spherical geometries if the function is solely dependent of the interface position.

Function describing how the (surface) energy function varies with the particle radius and/or the interface velocity.

The classical expression for the surface energy contribution has the form of .

The molar volume should be given relative to the molar volume used by default in DICTRA, 1 x 10^-5 (m³/mole). The volume should also be given per mole of substitutional atoms. For a precipitate of type M_xC_y this means multiplying with a factor (y+x)/x. If we use M₆C as an example with surface tension 0.5 (J/m²) and molar volume of 0.71 x 10^-5 (m³/mole), the entered function should be 2*0.5*0.71*(7/6)/X;

Commonly the surface tension function is defined as:

delta-G = 2 * SIGMA * Vm / R

The function to be entered will then be:

2*SIGMA/X;

A limited interface mobility can be expressed as:

delta-G = v * Vm /const

The function to be entered is then:

v/"const";

The expression is multiplied by the partial molar volume of the substitutional components.